For drivers to put in a full range imperial inexpensively, I would use a Peavey Scorpion, http://www.zzounds.com/item--PEVSP1525 for the bulk of the sound, and whatever cheap 15” sub you can find for the other driver. I have a car sub in my imperial, and it loads the horn well.

J-Rock,Build the imperial out off exterior grade plywood which is ugly but cheap (er). Put some exterior grade paint on it to hide the ugliness. Parts Express has an eminence woofer on closeout that is priced right and actually has good specs for the Imperial;

You could always go the cardboard route, but for outside that sounds iffy.

I understand wanting to build one (I've build two) and also the budget issue, but the other thing to think about is how much time you will invest in building and whether you want to invest that time to build something that's good or crappy. I thought about using cheap plywood (they are for PAs after all), but stumbled on to a deal with maple 13-ply for $28 a sheet. I think it took 5 sheets for a full size imperial so even with that awesome deal it's still $150 US for the wood. Then there's the glue, screws, biscuits, grills, wiring, binding posts, crossover, etc.

I'm certainly not trying to discourage you. I think with some skillful scrounging you could make one on the cheap and be happy with the results.

as far as wood, screws and other hardware, I have no problem with that, I have it all already, I just am trying to find some good cheap woofers. And I doubt I will spend more than one day in the shop building an pair. I have no problem making WOs and DBs in an hour, so i figure and imperial should take me around 4 to 5 hours. so a good day of work for a pair.

Would you recommend that eminence driver in a half Imperial? Or two in each imperial?

I may just build the imperials and test them out with some car subs I have and see how they sound. I just doubt the car subs can get as high as necessary to cross over to the hifrequency horn.